asynctask 函数无法识别结果值

Posted 2023-05-07

【中文标题】asynctask 函数无法识别结果值

【英文标题】：the asynctask function is not recognizing the result value

【发布时间】：2019-10-13 11:57:18

【问题描述】：

我通过 AsyncTask 访问 JSON，但是在 onPostExecute 中，String 结果没有得到结果值。

我希望它读取 json 并返回值“perfil”，然后将 new 发送到主要活动

归功于谷歌翻译......

访问 MainActivity 到 MecanismoString

String login = textousuario.getText().toString();
            String senha = textosenha.getText().toString();
            String urllogin = "http...."
            String tipo = "";
            MecanismoString mecanismoString = new MecanismoString(this, this);
            mecanismoString.execute(tipo, urllogin, login, senha);

Asynctask MecanismoString

public class MecanismoString extends AsyncTask <String, String, String> 

    private Interfacestring Interfacestring;
    private RequestQueue requestQueue;
    private StringRequest request;
    private Interfacestring execinterface;

    String usuario, senha, result;

    Context context;
    Toast toast;

    public MecanismoString (Context context, Interfacestring execinterface)
        this.context = context;
        this.Interfacestring = execinterface;
    




    @Override
    public String doInBackground(String... params) 

        Log.i("Script", "1 ->" + params[0]);
        Log.i("Script", "2 ->" + params[1]);
        Log.i("Script", "3 ->" + params[2]);
        Log.i("Script", "4 ->" + params[3]);

        usuario = params[2];
        senha = params[3];

        requestQueue = Volley.newRequestQueue(context);

        request = new StringRequest(Request.Method.POST, params[1], new Response.Listener<String>() 
            @Override
            public void onResponse(String response) 
                try 
                    JSONObject jsonObject = new JSONObject(response);

                    result = jsonObject.getString("perfil");


                 catch (JSONException e) 
                    e.printStackTrace();
                

            
        , new Response.ErrorListener() 
            @Override
            public void onErrorResponse(VolleyError error) 

            
        )
            @Override
            protected Map<String, String> getParams() throws AuthFailureError 
                HashMap<String, String> hashMap = new HashMap<String, String>();
                hashMap.put("login", usuario);
                hashMap.put("senha", senha);

                return hashMap;
            
        ;

        requestQueue.add(request);

        return (result);
    


    @Override
    protected void onPostExecute(String result) 

        execinterface.carregarString(result);

    

返回 MecanismoString 值的代码

public void carregarString(String result) 

        Toast.makeText(context.getApplicationContext(),
                result,
                Toast.LENGTH_SHORT) .show();

    

错误日志

E/androidRuntime: FATAL EXCEPTION: main
    Process: ic.eng.br.eunaobra, PID: 13735
    java.lang.NullPointerException: Attempt to invoke interface method 'void ic.eng.br.eunaobra.Interfacestring.carregarString(java.lang.String)' on a null object reference
        at ic.eng.br.eunaobra.MecanismoString.onPostExecute(MecanismoString.java:94)
        at ic.eng.br.eunaobra.MecanismoString.onPostExecute(MecanismoString.java:22)
        at android.os.AsyncTask.finish(AsyncTask.java:695)
        at android.os.AsyncTask.-wrap1(Unknown Source:0)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:712)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6944)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
I/System.out: (HTTPLog)-Static: isSBSettingEnabled false
    (HTTPLog)-Static: isSBSettingEnabled false
I/qtaguid: Untagging socket 76 failed errno=-22
W/NetworkManagementSocketTagger: untagSocket(76) failed with errno -22
Application terminated.

【问题讨论】：

在 MecanismoString 构造函数中我认为你没有正确引用接口

试试这个公共 MecanismoString (Context context, Interfacestring execinterface) this.context = context; this.execinterface=执行接口；

也是一个错误，重复界面，但继续出现此错误：java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on空对象引用

【参考方案1】：

请传递正确的上下文和 execinterface 对象：

MecanismoString mecanismoString = new MecanismoString(MainActivity.this, correct execinterface object);

请从carregarString()中删除getApplicationContext()，因为您已经拥有context：

 public void carregarString(String result) 
        Toast.makeText(context,result,Toast.LENGTH_SHORT) .show();
    

【讨论】：

声明对象而不是“this”时的错误，更改了“Toast”，但错误仍然存​​在：java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android. content.Context.getPackageName()' 在 android.widget.Toast.

的空对象引用上

对不起，我看不懂你刚才写的东西，你能不能说得清楚一点？

n 总结，我需要结果值，它位于 InBackground 内部，以便在 onPostExecute 中接收，但我做错了什么......我无法将字符串结果发送到 onPostExecute

你能不能返回 result 而不是 (result) ？并在回行处打断点，看看结果是否生成良好

我发现了错误，我卸载了整个过程。我在吐司。 ` toast = Toast.makeText(this, result, Toast.LENGTH_SHORT); toast.show();` 现在我正在重新插入 JSON